Romney still retains a decisive edge in the delegate count that will determine the GOP nomination, but the race is likely now prolonged for weeks, thwarting Romney's hope to put the intramurals behind him and shift focus to the incumbent.

Romney tried to signal that while he wasn't taking the nomination for granted, he expected to prevail and would be turning toward the fall and the battle against Barack Obama. He was magnanimous toward his GOP rivals and venomous toward the Democratic president.

“We're counting up the delegates for the convention, and it looks good. And we're counting down the days until November, and that looks even better,” Romney told a hotel ballroom with hundreds of chanting, cheering supporters in Boston, where he served as governor. “I stand ready to lead our party, and I stand ready to lead our nation to prosperity.”

Ohio was the most hotly contested prize and as Romney and Santorum battled in an extremely close race. Each was poised to win delegates from the state, and it was possible that even if Santorum won the popular vote, Romney would take more delegates.

But many Republican voters don't seem willing to hand him the reins quite yet, though he scooped up dozens of delegates in his home state and in Virginia, where only Lake Jackson Rep. Ron Paul also managed to get on the ballot.

Tennessee in particular renewed Santorum's prospects — a major battleground and a Southern state to boot.

Romney “can't spend a lot of time focusing on Obama if he's still fighting off Santorum and Gingrich,” said Whit Ayers, a top GOP strategist who supported former Utah Gov. Jon Huntsman.

Santorum, watching election returns in Steubenville, Ohio, not far from his home turf in Pittsburgh, left no doubt that he'll keep plugging away.

“We have won in the West, the Midwest, and the South, and we're ready to win across this country,” he told supporters. “When they thought, ‘Oh, OK, he's finally finished,' we keep coming back. We are in this thing.”

Gingrich bet almost entirely on Georgia, the state he represented in Congress. His only victory since South Carolina in late January let him avert a campaign-ending embarrassment and turn his attention to other Southern states.

“Tomorrow will bring another chapter in the race for the nomination,” he declared in Atlanta.

Even before Tuesday night's results came into focus, Santorum supporters rejected the inevitability argument for Romney and disputed that delegate math is the key measure until the field winnows further.

“If you have a true two-person race, Romney's still not getting close to 50 percent,” said Stuart Roy, a GOP strategist and adviser to Red, White and Blue Fund, the pro-Santorum Super PAC.

He shrugged off concerns that Romney — or Santorum, for that matter — already is wounded heading into the fall, citing polls that show either within striking distance of an unpopular president.

The Ohio Democratic Party issued a memo Tuesday asserting that Romney hurt his prospects badly by pandering to the right wing in his quest to close out the race, and especially by sticking by his criticism of the federal auto industry bailout.

“In a general election, when you're appealing to Democrats and independents, that will be an issue,” said political scientist Herb Asher, a longtime analyst of Buckeye politics at hio State University. “The better GM and Chrysler do, the easier it becomes for Democrats to say, if they had been president, GM and Chrysler would no longer exist.”

Until Romney has the playing field to himself, he's stuck fighting on two fronts.

“Eventually the delegate math becomes compelling, and he's just about there,” said Anthony Corrado, a political scientist at Colby College in Maine. “Certainly no later than March 20 in Illinois. The delegate math will make it impossible for anyone else to become the nominee.”